This application is a 35 USC 371 application of PCT/DE 00/02408 filed on Jul. 22, 2000.
1. Field of the Invention
The invention relates to a fuel injection system for an internal combustion engine, having a fuel high-pressure reservoir, from which an injection line for the fuel to be injected and a drive line for fuel branch off, which fuel is used as a first working medium.
2. Description of the Prior Art
One fuel injection system of the type with which the invention is concerned is already known from German Patent Disclosure DE 44 07 585 A1 and is based on an injection system known by the name xe2x80x9ccommon railxe2x80x9d. In this injection system, a cylindrical pressure container is used, to which fuel is delivered by a high-pressure pump. The high-pressure reservoir serves essentially as a buffer, which damps pressure fluctuations that result from the delivery of the fuel by the high-pressure pump and the withdrawal of the fuel by the injection nozzles.
From the above reference, it is known for the fuel present in the high-pressure reservoir to be used for actuating a hydraulic valve controller. To that end, the fuel is first delivered by the drive line to a hydraulic chamber, with which an outlet valve is associated and which is controlled by two control valves, and then to a hydraulic chamber which is associated with an inlet valve and is also controlled by two control valves. By suitable switching of the control valves, the inlet valve and the outlet valve are opened counter to the action of a conventional valve spring and closed again by means of the valve spring.
The fuel injection system according to the invention, has the advantage that an external consumer, which is actuated not with the fuel itself but rather with an arbitrary other, second working medium, can be connected to the high-pressure reservoir. The converter makes it possible to put the second working medium under a pressure that differs from the fuel pressure.
In one advantageous embodiment of the invention, it is provided that the converter has a translationally displaceable inlet piston and an actuator, by which the inlet piston can be acted upon periodically by fuel under pressure. In this way, at little structural expense, it is possible for the potential energy stored in the fuel under pressure to be converted into a reciprocating motion of the inlet piston, which can then in turn be converted into a volumetric flow of a second working medium that is under pressure.
Preferably, it is provided that the actuator is a 3/2-way valve. Such valves are available in the form of reliable mass-produced components, making the expense for controlling the inlet piston minimal.
In a preferred embodiment of the invention, it is also provided that the converter has a translationally displaceable outlet piston, which is connected to the inlet piston, and two check valves associated with the outlet piston. The outlet piston acts on the order of a piston pump that is driven directly by the inlet piston. Thus a loss- free conversion of the driving energy furnished by the inlet piston is obtained.
Preferably, the cross section of the inlet piston differs from the cross section of the outlet piston. In this way, a conversion of the pressure of the fuel, which is used as a first working medium, into a higher or lower pressure of a second working medium can be attained. For instance, if the cross section of the inlet piston is smaller than the cross section of the outlet piston, then a lesser pressure in the second working medium and a higher volumetric flow, compared to the fuel, are attained. Conversely, if the cross section of the inlet piston is greater than the cross section of the outlet piston, a higher pressure than in the fuel can be attained in the second working medium, although in that case a lesser volumetric flow is available.
In a preferred feature of the invention, a high-pressure reservoir for the second working medium can be provided. This high-pressure reservoir functions similarly to the fuel high-pressure reservoir, in that pressure fluctuations resulting from the delivery of second working medium to its reservoir are damped. Furthermore, withdrawal of the second working medium from its reservoir also leads to only a negligible pressure change in this reservoir, so that this reservoir furnishes the second working medium at an essentially constant pressure.
Furthermore, two converters can be provided, which operate in alternation. In this way, pulsation of the pressure in the second working medium can be further reduced, since a virtually constant pumping of the second working medium is attainable.